Humans and chimps more genetically similar than mice and rats

While reading a review on the genomic comparisons of brain evolution (get ready!), one line jumped out at me from the introduction:

"Genetically, humans are close to other apes: the genetic distance between humans and chimpanzees or bonobos is on the order of 1–5% (depending on the types of genetic divergence considered) and reflects the recent divergence of the species. By comparison, the difference between the common mouse and rat species, Mus musculus and Rattus norvegicus, respectively, ranges from 20% to 50%."

- M. Somel, X. Liu and P. Khaitovich (from 'Human brain evolution: transcripts, metabolites and their regulators,' Nature Reviews Neuroscience, 2004).

The authors indicate that the common mouse and rat have a ~10x greater genetic difference between their genomes than do humans and chimpanzees/bonobos. While I'm not an expert on mice or rats (or chimpanzees or humans), intuitively, humans vs. chimpanzees/bonobos exhibit more significant differences in terms of morphology, ecology and behavior than do mice vs. rats.

What, then, do the greater differences between mice vs. rats compared to humans vs. chimpanzees indicate about the evolutionary context of the mouse/rat divergence?  Compared to other rodents, rats have many rat-specific segments of repeats; the mouse genome has a particular deletion of a gene possessed by other rodents, including rats. When similar ecological niches are ultimately occupied and behavioral/functional repertoires expressed by the two species, are these genetic differences evidence of a bottleneck or founder effect in a common ancestral population? Are the similarities given such genetic differences evidence of convergent evolution between the two lineages? How can these be teased apart?

Further reading:
Gibbs RA, Weinstock GM, Metzker ML, Muzny DM, Sodergren EJ, Scherer S, Scott G, Steffen D, Worley KC, Burch PE, Okwuonu G. Genome sequence of the Brown Norway rat yields insights into mammalian evolution. Nature. 2004 Apr 1;428(6982):493.
https://www.nature.com/articles/nature02426

Cooper GM, Brudno M, Stone EA, Dubchak I, Batzoglou S, Sidow A. Characterization of evolutionary rates and constraints in three mammalian genomes. Genome research. 2004 Apr 1;14(4):539-48.
https://genome.cshlp.org/content/14/4/539.full

Mackenzie Hepker